You might want to try it again, as it seems from other reports that there were some ftp related troubles about the time you were reporting having that error, and they appear to be "fixed" now.
First, forget about FrontPage. You use an FTP client program to upload the proper picture file into their appropriate directories. There are many free and excellent FTP clients downloadable from the web (check the DH wiki, or use Google), so you don't have to "buy" any new software.
If you goto the DreamHost wiki (http://wiki.dreamhost.com) and explore the "Getting Started pages and the FTP related pages, you can learn a lot about how all this works together to put stuff on the web.
How you "get into" the right directory to do the upload depends on the FTP program you choose to use, but most of them are simple graphical user interfaces (usually paned windows) showing you files and "folders" (really they are directories) on your "local" computer and on the "remote" computer (the server to which you are connected, in this case DreamHost).
In most cases you simply double-click on a folder in the "remote" window pane, and the program enters that folder and displays it's contents. Once you are "in" the correct folder on the "remote" computer, you can usually either "drag-n-drop" from the "local" computer's window pane to the "remote" computer's window pane (this is "uploading").
You can also usually tag and click files (or groups of files) in the local computer display and then issue a command (from a menu or with a pop menu via a right mouse-click) to "upload" the file(s). When you do this, the files are sent to the directory ("folder") you are in as displayed in the remote window. There is more, but hose are the essentials. Take a look at the help files for the FTP client you choose to use, and you should be able to figure it out.
BTW, DreamHost support was actually doing you a huge favor by suggesting you abandon Fr*ntPage. It is a "dead" product tha even it's mother doesn't support any more and, while it worked "reasonably well" at one time for many, it's continued use, and you relying on it, is only going to lead to more frustration for you. Hey, old Commodore 64 was a "great computer" in it's day, but it's not suitable for surfing the web
This isn't the place to go into all of that, but you can find plenty of relevant information to explain why that is true by searching this forum or the web in general (Google is your friend).